Color dot screen with dot form compensation for apparent shift of beam deflection center

ABSTRACT

An optical system utilized for providing a tridot patterned color cathode ray tube screen wherein the dot patterns are modified in discrete screen areas to improve the registration of the electron beams with their respective phosphor dots thereby improving color purity of the display. The light source in the optical system used in effecting screen exposure has contiguously oriented light control means with portions formed to provide both symmetrical and unsymmetrical exposure illumination. Thus, by utilizing unsymmetrical exposure, patterns of elongated dots are disposed on different discrete portions of the screen for each of the respective phosphors to achieve improved beam dot registration.

United States Patent COLOR DOT SCREEN WITH DOT FORM COMPENSATION FOR APPARENT SHIFT OF BEAM DEFLECTION CENTER 4 Claims, 7 Drawing Figs.

US. Cl 313/928 Int. Cl Holj 29/32, H0 1 j 29/30 Field of Search 313/92 (B), 70 (C) [56] References Cited UNITED STATES PATENTS 2,757,231 7/1956 Law l78/5.4 2,947,899 8/1960 Kaplan 3/3/92 Primary Examin'erRobert Segal Attorneys-Norman J. OMalley, Robert E. Strausser and Frederick H. Rinn ABSTRACT: An optical system utilized for providing a tridot patterned color cathode ray tube screen wherein the dot patterns are modified in discrete screen areas to improve the registration of the electron beams with their respective phosphor dots thereby improving color purity of the display. The light source in the optical system used in effecting screen exposure has contiguously oriented light control means with portions formed to provide both symmetrical and unsymmetrical exposure illumination. Thus, by utilizing unsymmetrical exposure, patterns of elongated dots are disposed on different discrete portions of the screen for each of the respective phosphors to achieve improved beam dot registration.

PATENTED MAYZS sum 1 or 5 TUBE AXIS m w m N I KENNETH L. STAUNTON ATTORNEY PATENTEU HAY25I97I 3581; 136

sum 2 OF 5 46 n l9 A 57 f 47 43 33 3s l8 was PRIOR ART Y W 9|" 211g. 7 KENNETH C."Z8fim- ATTORNEY PATENTEU HAYES I971 SHEET 3 [1F 5 IN VENTOR. KENNETH L. STAUNTON fp m 72.6101

ATTORNEY PATENTEU MY 2 51% SHEET 5 BF 5 ATTORNEY COLOR DOT SCREEN WITH DOT FORM COMIPIENSATION FOR APPARENT SHIFT OF BEAM DEFLECTION CENTER BACKGROUND OF THE INVENTION The invention relates to cathode-ray tubes and more particularly to improved patterned multiphosphor screens and an optical system utilized in forming improved screens for color cathode-ray tubes.

Color cathode-ray tubes utilized as display devices in television applications, conventionally employ one or more electron guns to furnish the required electron beam or beams which are accelerated, focused and modulated by voltages applied to the respective gun. When a plurality of related guns are utilized in a common assembly, conveyance electrodes or pole pieces are usually included as part of the electron gun structure. In operation, the modulated electron beams are deflected across the cathodoluminescent screen to selectively impinge certain of the color-fluorescing materials disposed in patterned configurations on the receiving panel of the tube, thereby reproducing the transmitted color image. It is conventional practice to position a grid or grids or an apertured mask intermediate the electron gun structure and the screen to provide focusing and deflection of the electron beams or selected masking of the screen.

Color cathode-ray tubes, of the type generally used in color television, usually employ screens consisting of multitudinous dot, bar or stripelike patterns of green, blue, and red color fluorescing electron-responsive phosphors. A number of methods have been used to fabricate the respective screens, for example, one conventional procedure utilizes a photoprinting technique. By this method, the viewing panel of the tube is coated with a light sensitive substance and one of the desired phosphor materials. The screen coating is then ex posed to a source of light through an appropriate negative master and suitably developed in a subsequent step to produce a first phosphor pattern of desired configurations. This procedure is repeated for each of the remaining color-emitting phosphors comprising the patterned screen. In the disposal of each respective pattern, the source of light is appropriately offset during the exposure operation to provide individual phosphor patterns that are properly displaced from one another to form the desired screen structure.

A difficulty encountered. with photodisposed screens is caused by the electron beams not following the same beam paths during tube operation as the light rays travel during the screen forming procedures. As a result, there are areas of the screen where the'electron beams do not properly impinge the desired patterned phosphor configurations during tube operation. This undesirable condition of misregister results in a display image having color impurity.

The inherent nature of the electron beam is a factor affecting the aforementioned condition of beam-dot misregister. Since the electrons projected toward the screen have mass and charge, their paths of travel are altered by the electron gun and tube geometry and by the various electrostatic and magnetic fields existing in and around the tube. It has been found that the center of deflection, or the location within the deflection yoke from which the electrons appear to come, moves as the electron beam scans the screen. Additionally, when several electron guns are employed to effect a plurality of beams, the phenomena resulting from the dynamic convergence of the several beams causes a departure of the beams from their usual paths of travel.

Various procedures and devices for reducing the amount of misregister between the electron beam or beams and thefluorescent phosphor patterns have been employed. Auxiliary devices have been utilized both internally and externally of the tube and on and about the tube components in an effort to compensate for the excursion of the electron beams from the desired trajectories. From the standpoint of screen exposure devices, several light optical systems have been devised to consummate photodeposition of the respective screen patterns. By way of example, in those: tubes having a dotted screen pattern formed relative to an apertured shadow mask wherein a triad of different phosphor dots is related to each aperture in the mask, several types of light-refractive means or lens componentshave been incorporated into the light optical system. For instance, in color cathode-ray tubes utilizing a 70 angle of deflection, it has been found that use of a light source in conjunction with a spherical symmetrical planar-concave lens, properly tilted and offset, provides light optics which substantially duplicate the electron optics of the operating tube as effected by the axial motion of the center of deflection and dynamic convergence. Screen exposure systems of this type are described and claimed in U.S. Pat. No. 2,986,000 issued to Glen A. Burdick, and U.S. Pat. No. 2,936,683 issued to Glen A. Burdick et al., both of which are assigned to the same assignee as the present invention.

In color tubes having angles of deflection greater than 70, for example, in rectangular tubes having deflection, it has been found that employment of the aforementioned lens in photodisposing the screen does not fully achieve the desired register relationship between light optics and electron optics. There are at least two areas of the rectangular screen, in substantially the upper rightand upper left-hand corner areas, wherein the desired spacings of dots in the triads are not fully realized. A related condition exists in the 70 tube exposure optics, but due to the smaller angle of deflection the effect is not of a significant magnitude, and the dot pattern beam registration is substantially acceptable for all areas of the screen. In the screen of 90 tubes, the phosphor dots and electron beam landing patterns exhibit substantially desired registration on the major portion of the screen withthe exception of the two aforementioned areas in the upper corner regions of the viewed screen. In the upper right corner area the dots of one color phosphor tend to be displaced in an outward radial direction in their triadical pattern, and in the upper left corner area dots of another color phosphor are affected in a similar displaced manner.

OBJECTS AND SUMMARY OF THE INVENTION It is an object of the invention to reduce the aforementioned difficulties and to provide an improved screen for a shadow mask color cathode-ray tube having improved registration of electron beam impingement on the phosphor dot pattern.

Another object is to provide an improved light optical exposure system for producing patterned screens for color tubes wherein the phosphor dots of the screen pattern are formed to effect improved registration with the respective electron beam landings thereon.

The foregoing objects are achieved in one aspect of the invention by the provision of an improved light optical system for photoprintingan improved color cathode-ray tube screen having a patterned negative mask in spaced adjacency therewith. Light radiation for the exposure of each screen pattern is emitted from an appropriately positioned source of light having contiguously oriented light control means associated therewith. The light control means comprises a structure having a light-emanating aperture of which a portion is modified in a nonsymmetrical manner to provide unsymmetrical exposure illumination to at least one discrete portion of the screen to form elongated dots thereat. In this manner improved beam-dot registration of the respective phosphor pattern is achieved in that area of the screen.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I a sectional view of a color cathode-ray tube of the shadowrftask variety utilizing plural electron beams;

FIG. 2 is a section view showing the manner in which the electron beams are converged in the tube,

FIG. 3 is a partial plan view illustrating a prior art rectangular screen wherein the phosphor dots and electron beam landings are exaggerated in size;

FIG. 4 is a partial vertical section of a type of apparatus utilized in photodisposing patterned cathode-ray tube screens taken along the line 4-4 of FIG. 5;

FIG. 5 is a top plan view looking through the panel into the apparatus;

FIG. 6 is an enlarged portion of a section of FIG. 4 illustrating in an exaggerated manner, the photoexposure of a single phosphor dot with the light refractive medium eliminated to facilitate clarity; and

FIG. 7 is a plan view of the embodiment of the light control means utilized in FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS For a better understanding of the present invention, together with other and further objects, advantages, and capabilities thereof, reference is made to the following specification and appended claims in connection with the aforedescribed drawings.

With reference to the drawings, FIG. I shows a conventional plural beam color cathode-ray tube 11, of the shadow mask type, having a central axis 13 therethrough. Suitably positioned within the neck portion of the envelope 15 are three electron guns or emitters l6 oriented, for example, substantially 120 apart and equally spaced about the central axis 13 to provide a delta arrangement of electron beams l7, l8 and 19 respectively. Coil means in the form of yoke 20, positioned externally of the tube envelope, are employed to deflect the electron beams over the raster area. It is desirable that the several beams converge at the apertured shadow mask 21 and thence pass through the apertures 22 therein to discretely impinge the patterned cathodoluminescent screen 23 spaced therebeneath. The screen comprises a multitude of triadically arranged dots of green, blue and red color-emitting electron-responsive fluorescing materials disposed on the interior surface of the viewing panel 25. While a trigun shadow mask color tube is illustrated in FIG. 1, it is not intended to be limited thereto, as the invention to be described is also applicable in other types of image reproduction devices utilizing plural beams of radiant energy excitation.

Since the tube axis, the panel axis, and the electron gun system axis are substantially coincidental, it seems expedient for clarification in the description to denote these several reference axes as the central axis 13.

In order to achieve the desired convergence or crossover of the several beams at the apertures in the mask, external dynamic convergence means 27 are conventionally employed. With reference to FIG. 2, two of the three beams, 17 and 18 respectively, are shown to illustrate the aspects of dynamic convergence. The static convergence electron beam paths, l7 and 18, pass through points a and b respectively in the deflection region and proceed in an angular manner with relationship with the central axis 13 to converge and cross over at the apertured mask 21 and thence impinge the respective phosphor dots of the patterned screen 23. In deflecting the beams to an angle alpha (or) without the influence of the dynamic convergence means 27, the separate beams appear to emanate from points a and b and undesirably bring about convergence at a point short of the mask as at point (I). Utilization of the dynamic convergence means provides magnetic fields which shift the beam positions 17 and 18' radially outward in the deflection region to cause the beam positions 17 and 18 to appear to come from points cand d to provide the desired convergence crossover at the apertured mask. As the angle of deflection increases, the deflected electron beam appears to emerge from the deflection region at a point closer to the screen. For example, as the electron beam 17 is deflected from the static position to the convergence deflected beam path 17', the dotted line between a and c defines the locus of motion 29 of the apparent center of deflection. In like manner, movement of the related beam from the static beam path 18 to the convergence deflected path 18 defines the locus of motion of the apparent center of deflection as being along the dotted line between points b and d. The apparent center of deflection and the locus of motion thereof is different for each of the electron beams because of the different orientations of the respective electron guns in the tube.

The cathodoluminescent screen 23 is made of multitudinous triadical groupings of different color-emitting electronresponsive phosphor dots, 35', 36, and 37 respectively. Two representations of such triadical groupings are shown in FIG. 2, in the form of an axial grouping 31 and a radial grouping 33. The geometry of the tube is such that the three electron beam landings form a substantially equilateral triadical formation at the center of the screen and a modified triadical formation at the peripheral region thereof. With the optical system conventionally utilized for screen exposure, the photodisposed triadical phosphor dot patterns, while substantially equilateral over a major portion of the screen area, depart significantly from equilaterality in certain peripheral areas. This departure is particularly noticeable in tubes having wide angles of deflection, such as in excess of 70, for instance deflection in rectangular screen tubes. Such is illustrated in FIG. 3 wherein a fragmentary portion of a prior art rectangular screen 34 is shown from the viewpoint of an observer facing the viewing panel 25. Illustrative groupings of dots and beam landings are shown in exaggerated size. The axial dot grouping 31 has substantially equilateral placement of the phosphor dots 35, 36, and 37. When the electron beams 17, 18, and 19 pass through the mask apertures and make landings on the electron-responsive dots, the areas of impingement fluoresce in a color characteristic of the particular phosphor, such as green (G), red (R), and blue (B), respectively. In the upper screen region 41, the illustrated radial grouping 33 shows an outward radial displacement of the green phosphor dot 45 with reference to the adjacent red dot 46 and blue dot 47. The criticalness of this displacement is evidenced when the deflected beam 17' makes a peripheral oficenter landing on the green dot 45. A similar situation exists in the upper right screen region 51 where an exemplary upper right radial triad 43 has the red phosphor dot 56 radially displaced.

It has been found that the respective misplaced dots in the aforementioned corner regions of rectangular screens can be dimensionally modified or elongated during screen pattern exposure. This is achieved by utilizing the method and the specialized optical system of the invention wherein a nonsymmetrical light control means provides unsymmetrical exposure illumination to a discrete comer portion of the screen.

An optical exposure apparatus, such as shown in FIG. 4, is utilized to form the aforementioned dot patterned screen. It is desired to discretely dispose the triadical dot patterns in a manner whereby the subsequent electron beam landings will be in register therewith and have the largest possible minimum border of fluorescent material around each beam impinging position. Prior to the exposure of each of the several patterns comprising the screen, the screen-bearing surface, in this instance the inner surface of the viewing panel 25, is coated with a light hardenable photosensitive substance and a desired electron responsive color cathodoluminescent phosphor material, one for example being zinc-cadmium sulfide which fluoresces green, to form a photosensitive phosphor-associated film 61 thereover. Next, the apertured mask is temporarily positioned in spaced adjacency with the sensitized panel, whereupon the mated mask-panel assembly is suitably oriented on the exposure apparatus 63. Within this apparatus, there are means 65 and 65' for predeterminately positioning an optical system 67 comprising a light source 69, light control means 71 contiguously oriented therewith, and a light-refractive medium or lens 73. In the exposure step, discrete areas of the coated panel are subjected to light radiating from the light source 69 which in passing through the predeterminately oriented nonsymmetrical light control means 71 is refracted by the lens 73 and directed through the mask aperture 22 to impinge the photosensitive film 61. The areas of the photosensitive film which are exposed to the light radiation become hardened and adhere to the surface of the glass panel 25 forming an imprint of a first screen pattern of dots. Sequentially, a screen-developing step removes the intervening unexposed portions of the film shadowed by the solid portions of the mask structure wherein the panel is treated with a suitable solvent or developing fluid. The aforedescribed procedure is twice repeated to dispose the required red and blue phosphor dot patterns of the complete screen combination. For the separate exposure of each screen pattern, the light source, the light control means, and the light refractive medium are properly positioned and offset from the central axis, the optical system being shifted substantially 120 about the central axis 13 for each subsequent pattern exposure.

In viewing the screen from the exterior of the viewing panel 25 as shown in FIG. 5, several orientation designations or transversals are considered. The screen area is substantially divided into four quadrants referenced through the central axis 13 and defined by the 12-6 oclock minor screen axis AH and the 3-9 o'clock major screen axis LP whereof the l23 oclock area defines the first screen quadrant, the 9- l2 o'clock area the second quadrant, the 6-9 o'clock area the third quadrant and the 36 oclock area the fourth quadrant. Other screen designations in the form of additional orientation transversals, also referenced through the central axis 13, are denoted as the 2-8 o'clock screen diagonal EF and the 4-10 oclock diagonal CD respectively.

In referring to FIGS. 4 through 7, the essentials of the improved screen and the optical system 67 for disposing the same are shown in greater detail wherein the light refractive medium or lens 73 is positioned intermediate the light source 69 and the apertured shadow mask 21. As aforementioned, the locus of motion of the apparent center of deflection in the operating tube appears to move forward toward the screen as the angle of deflection increases. In a like manner, the apparent origin of the light source appears to follow a similar locus due to the refraction of the light by the lens 73. Light emanating from the light source and control means, as for example rays represented by lines 75 and 76, ultimately reach the photosensitive screen material to expose phosphor dot areas 77 and 78 respectively; there being diagonally opposite areas of the screen. The electron beams for the same deflection angle appear to originate at point M. Point N designates the apparent light source for a ray 80 beamed to the screen center dot area 81, whereof the apparent locus of motion of the light source falls along line M-N. With reference to FIGS. 2 and 4, the optical system of the exposure device produces the desired spacial relationship between the apparent center of electron beam deflection and the apparent origin of light beams to effect the desired register between the phosphor dot screen pattern and the respective electron beam impingements thereon. The optical system illustrated is capable of photodisposing, for example, a first color-emitting screen pattern whereof a dot in substantially the upper left corner or oclock area of the second screen quadrant of the viewed screen is designated as 77 and one substantially the lower right corner or 4 oclock area thereof as 78. The relationship of subsequent electron beam impingements on these respective phosphor dot areas are denoted in FIG. 5 as 79 and 79.

The improved. optical system of the invention for photodisposing the patterned screen of a 25-inch rectangular shadow mask tube having substantially 90 deflection, utilizes a light control means 71 which is contiguously oriented to the light source 69. The control means is fashioned as a collar 83 having an aperture 85 therein shaped to surround the emitter 70 of the light source 69. The aperture is formed in a symmetrically modified manner wherein at least one modified lightemanating portion extends in a substantially radial manner from the axis 86 of the aperture and is formed substantially as a slot 89 having a longitudinal plane of symmetry 91 therein whereby unsymmetrical exposure illumination is provided to a discrete portion of the screen. It has been found that use of the light control means with the symmetrically modified aperture effects an unsymmetrical masked light source which increases the exposure illumination directed, in this instance, to the upper left or second quadrantal area of the screen to expand the area of light ray landings radially inward thereby providing substantially localized deposition of elongated green-emitting phosphor dots to enhance subsequent registration with the respective electron beams directed thereto.

It has been found that the orientation of the optical system 67 to produce the aforedescribed modified or elongated dots in the 25 inch rectangular panel is accomplished by orienting the axes of the components comprising the system in a common vertical plane containing the central axis 13. The light source axis 68 which is common to that of the control means is laterally offset from the central axis by the distance k. Since the structure and detailed orientation of the light refractive medium or lens 73 do not substantially influence the desired functioning of the light control means of the invention, delineation of lens details will be eliminated from this specification and the drawings relating thereto.

in this specification several phosphor dot patterns are considered as first G, second R and third B color-emitting phosphor patterns respectively. The numerical designations are intended to denote the different phosphors and not the order of pattern deposition.

With particular reference to FIGS. 4, 5, and 6, looking into the viewing panel 25 positioned atop the exposure apparatus 63, positioning planes utilized in orienting the optical system 67 for photodisposing the several color-emitting phosphor patterns are indicated. For example, the first phosphor colorfluorescing dot pattern is formed by positioning the optical system in the plane CD which substantially corresponds to the 4-l0 oclock screen diagonal, being removed clockwise from the l26 oclock minor screen axis in the ordinate plane AH by The plane of symmetry 91 of the slot in the light control means 71 is positioned coincident with plane CD which also contains the central and light source axes, 13 and 68 respectively. The symmetrically modified portion or radial slot of the aperture is oriented to direct additional exposure illumination to the upper left or peripheral 10 oclock screen sector area 41 of the second screen quadrant to dispose an elongated first phosphor color-emitting dot pattern in that discrete screen area.

With particular reference to FIG. 6, wherein the light refractive medium is omitted to enlhance clarity, there is shown an enlarged portion of FIG. 4 exaggerating the photoexposure of a single phosphor dot 77. The light control means without a slot would emanate symmetrical exposure illumination from the emitter 70 having a diameter of r. The light beam 93 therefrom would have a dimension of s and when passing through aperture 22 in the mask 21 would dispose a phosphor dot having a diametrical dimension of v. By utilizing the slot portion 89 of the modified aperture, additional exposure light increases the beam to the dimension of r which increases the area of light beam impingement radially toward the central axis 13, thus elongating the dot dimension to a. The elongated first phosphor dot forms part of the triadical grouping along with the regularly formed second and third phosphor dots 94 and 96 respectively. The maximum dot elon gation is in the peripheral area 41 along the plane CD in screen quadrant 2, with the dot elongation diminishing in a gradual manner on either side therefrom. The unmodified or symmetrical portion of the light control means provides substantially symmetrical light for substantially equilateral first phosphor dot pattern exposure on the remaining area of the sensitized screen panel.

In photodisposing a second phosphor dot pattern, the optical system is positioned along plane EF which substantially corresponds to the 28 o'clock screen diagonal, being removed clockwise from the 12 oclock position by 240. In FIG. 5 the whole optical system is shifted to coincide with the plane EF. The light source is indicated at 69a and the light control means 71 is oriented with the longitudinal plane of symmetry of the modified portion coinciding substantially with the plane EF. The screen exposure illumination emanating from the symmetrical portion of said light control means provides substantially equilateral second phosphor dot pattern exposure on substantially all areas of the screen except substantially the peripheral portion of the 2 oclock screen sector area 51. in this discrete screen area the additional exposure illumination passing through the slot portion 89 of the light control means provides second phosphor dot pattern 95 that is elongated in a radial manner to afford more area for electron beam impingement and thereby enhance registration and resultant color purity.

For third phosphor dot deposition the optical system is oriented in the AH'or minor axis plane wherein light source 6917 is indicated. With the optical system so positioned, exposure improvement would fall mainly within the area 101 which is substantially outside of the rectangular screen and requires no dot shape modification but in a round screen 106 modification of the third phosphor dot pattern would be desired in that area to improveregistration. However, in rectangular screens, there are two small screen areas in the lower right 103 and the lower left 105 wherein registration improvement is beneficial. This improvement is in the form of third phosphor elongated dots and is brought about by maintaining the same optical system orientation and utilizing a light control means 71' having dual symmetrically modified light control portions or slots 89 and 89' in common plane of the collar with the respective longitudinal planes of symmetry oriented at least 90 apart. The slots are positioned that each of the planes of symmetry substantially coincide with separate vertical planes ST and UV which are extended from said light source axis 69b in angular relationship with the l26 o'clock transversal to form substantially equal angles [3 and B of at least 45. The angular values being derived by positioning planes ST and UV in a manner to substantially bisect the corner areas 103 and 105 respectively. In these areas, the elongation of the third phosphor dot pattern is related radially with the axis of the light source.

With reference to FIGS. 6 and 7, one embodiment of the light control means is further detailed. It has been found that a slot width y of approximately .070 inches is satisfactory for dot modification in the 19- and 25-inch rectangular panels. The length z should be of an adequacy to allow unobstructed passage of light radiation from the emitter 70, while the thickness x should be sufficient to prevent heat warpage during usage.

Thus, in rectangular cathode-ray screens of the type described, specific elongated dot patterns in discrete portions of the screen are expeditiously achieved. This results in a color display of improved color purity since certain of the color dot patterns are more desirably formed in these screen areas to be in better register with electron beam impingement.

While there have been shown and described what are at present considered the improved embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

lclaim:

1. An improved screen for a color cathode-ray tube having a central axis, a plurality of off-axis electron guns, an apertured shadow mask and a related tridot screen having improvement means therein to enhance beam-dot registration and to compensate for the apparent movement of the centers of deflection of beams emanating from said off-axis guns, said screen area being divided into quadrants defined by the l26 oclock and 39 oclock screen axes whereof the 12-3 o'clock area defines the first quadrant, the 9-12 o'clock area the second quadrant, the 6-9 oclock area the third quadrant and the 36 oclock area the fourth quadrant, said screen improvement comprising a plurality of first, second, and third color-emitting phosphors disposed in related dot patterns whereof the dots of at least one color-emitting phosphor are elongated in a substantially radial manner in at least one quadrant including a plane passing through said central and resfective gun axes.

. A cathodolummescent screen according to claim 1 wherein the dots of said first phosphor pattern are substantially elongated in a discrete substantially peripheral portion of said second screen quadrant.

3. A cathodoluminescent screen according to claim 1 wherein the dots of said second phosphor pattern are substantially elongated in a discrete substantially peripheral portion of said first screen quadrant.

4. A cathodoluminescent screen according to claim 1 wherein the dots of said third phosphor pattern are substantially elongated in discrete substantially peripheral portions of said third and fourth screen quadrants. 

1. An improved screen for a color cathode-ray tube having a central axis, a plurality of off-axis electron guns, an apertured shadow mask and a related tridot screen having improvement means therein to enhance beam-dot registration and to compensate for the apparent movement of the centers of deflection of beams emanating from said off-axis guns, said screen area being divided into quadrants defined by the 12-6 o''clock and 3-9 o''clock screen axes whereof the 12-3 o''clock area defines the first quadrant, the 9-12 o''clock area the second quadrant, the 6-9 o''clock area the third quadrant and the 3-6 o''clock area the fourth quadrant, said screen improvement comprising a plurality of first, second, and third color-emitting phosphors disposed in related dot patterns whereof the dots of at least one color-emitting phosphor are elongated in a substantially radial manner in at least one quadrant including a plane passing through said central and respective gun axes.
 2. A cathodoluminescent screen according to claim 1 wherein the dots of said first phosphor pattern are substantially elongated in a discrete substantially peripheral portion of said second screen quadrant.
 3. A cathodoluminescent screen according to claim 1 wherein the dots of said second phosphor pattern are substantially elongated in a discrete substantially peripheral portion of said first screen quadrant.
 4. A cathodoluminescent screen according to claim 1 wherein the dots of said third phosphor pattern are substantially elongated in discrete substantially peripheral portions of said third and fourth screen quadrants. 